1. Field of the Invention
This invention relates to an improvement in a traditional brake cable-fixing device for a parking brake, in which the improvement affords an easy, effective and efficient installation of the brake cable onto a brake lever.
2. Description of Related Art
FIG. 8 shows a conventional mechanical shoe actuating mechanism as is disclosed in the U.S. Pat. No. 5,311,793, the disclosure of which is hereby incorporated by reference. This mechanism involves components comprising a strut (pressure bracket) a, a brake lever (actuating lever) b, a plate spring (elastic spring leg) c, and a brake cable d.
The strut a has a space a1 formed from its intermediate portion toward its left end, and the brake lever b positioned in the space a1 is pivotally supported by a pin e.
In addition, the left bottom side of the space a1 is formed in a rectilinear shape. The strut a has a plated section at its right side, and a notched groove a2 is formed at the middle of the plated section. A right brake shoe (spacing lever) f engages the notched groove a2.
The brake lever b is an integration of two plates, wherein forked legs are formed at each right end with a gap b1. The gap b1 is so designed and sized to permit an inner cable d1 of the brake cable d to pass through, but a nipple d2 fixed to the top end of the brake cable d is blocked against passage through the gap b1. Therefore, the nipple d2 is hooked on a groove b2 formed on the forked legs.
The left side of the brake lever b is positioned between two unconnected facing plates of the strut a (see FIG. 8B) and is pivotally, rotatably supported with respect to the strut a by the pin e. The brake lever b has an engagement groove b3 adjacent to that pivot section and engaged with a left brake shoe g.
The plate spring c is in the shape of an open clasp comprised of a pair of elastic spring legs c1, c2, each connected at one end with a vertex. One elastic spring leg c2 is urged against curved outer edges b4 of the forked legs at the free end of the brake lever b closing a gap between the curved outer edges b4 and the space a1, and the other elastic spring leg c1 opposite to the elastic spring leg c2 angled at its free end is hooked on the right bottom of space a1 of the strut a.
When the brake cable d hooked on the brake lever b upwardly in FIG. 8A is pulled, the brake lever b rotates counterclockwise with respect to the pin e, thereby pushing the brake shoe g to the left and pushing the brake shoe f to the right by a reaction force thereof, and thereby rotating the pair of brake shoes f and g to spread apart.
The brake cable d is installed on the brake lever b in the following manner. The brake cable d is inserted from an upper part of the FIG. 8A, and the nipple d2 advances in the space a, along the curved outer edges b4 of the brake lever b at its free ends, deflecting the elastic spring leg c2 of the plate spring c.
As the brake cable d is further pushed toward the elastic spring leg c2 so as to cause the nipple d2 to slide along and pass the curved outer edges b4 of the brake lever b, the nipple d2 is snapped in and is positioned to be engaged with the groove b2 of the brake lever b by a restoring force exerted by the elastic spring leg c2. Accordingly, the brake cable d is positioned between the forked legs of the brake lever b while the nipple d2 is positioned on the groove b2 of the brake lever.
When the spring leg c2 of the plate spring c is attached to the spring leg c1, a gap between the spring leg c2 and the curved outer edges b4 of the brake lever b must be sufficient for the nipple d2 to be passed through.
With reference to FIG. 8A, if the letter L stands for a distance from a pivot point between the strut a and the brake lever b to a position where the brake cable d is pulled, and if the letter H stands for a distance from the pivot point between the strut a and the brake lever b to the brake shoe g, a lever-ratio in the mechanical shoe actuating mechanism may be represented as L/H.
Effectiveness of the parking brake may be improved if the lever-ratio in the mechanism for mechanical operation becomes higher by setting the entire length of the strut a and the distance L from the pivot point between the strut a and the brake lever b longer. However, such a design causes a problem of enlarging the mechanism and a problem of complexity of the layout in the drum brake.
On the other hand, if the mechanism is downsized and the distance L is shortened, the lever-ratio becomes smaller ultimately reducing the effectiveness in an undesirable manner. The need therefore exists for a brake cable-fixing device that is smaller in size without sacrificing lever-ratio.
This invention was made to improve the above-points, and its object is to provide a brake cable-fixing device for a parking brake pursuing a downsized mechanism with the larger lever-ratio.
In accordance with this invention, an entire length of the strut may be shortened without lowering the lever ratio of the mechanical shoe actuating mechanism by designing the space formed between two facing plates of the strut such that its upper half side is longitudinally wider than its lower half side. Therefore, this invention enables to design the mechanism not only to be smaller but also to improve the lever-ratio at the same time.
Since an entire length of the mechanical shoe actuating mechanism is substantially shortened and compactly designed, this invention is suitable for a drum brake utilized in a small size vehicle and has a significant economic effect.
The space of the strut may be formed simultaneously at the time the strut is formed by press. This facilitates the forming process and reduces the manufacturing cost.
The grooves on one ends of brake lever and the nipple of the brake cable are designed to be semicircular, thus providing an engagement between the facing surfaces and allowing smooth movement. Therefore, durability of the engagement section increases, and the inner cable under the nipple is not repeatedly deflected when operating the parking brake.
This invention maintains a low amount of horizontal movement in the pivot section between the brake lever and the strut even if the section makes a slight yawing movement, thereby providing assured engagement of the nipple and the inner cable with the brake lever.
A funnel-shaped or flared-out portion may be formed at an entry portion of the strut into which a nipple of the brake cable is inserted. This facilitates an insertion of the nipple into a drum brake already installed onto the vehicle with a brake drum and gives superior brake cable installability.